A battery case for securing and mechanically isolating a battery from a vehicle having an OEM battery holder. The battery case includes an adapter for securing the battery case to the vehicle. The adapter is configured for placement within a receiving cavity defined by the OEM battery holder. The adapter has a footprint that is substantially identical to the footprint of the battery. The adapter further has securement features that are substantially identical to the securement features on the battery. The battery case further includes a lower battery containment plate for supporting the battery thereon. The battery case still further includes at least one shock absorbing element positioned between the adapter and the lower battery containment plate for absorbing shocks and vibrations received from the vehicle so as to mechanically isolate the battery from the vehicle. The battery case still further includes an upper battery containment plate for placement over the battery for retaining the battery between the lower and upper battery containment plates.